In general, edible fats and oils purified by a conventional method are almost tasteless and odorless in comparison with special fats and oils such as sesame oil, olive oil, cacao butter and the like. An oil produced by flavoring or seasoning such a purified edible fat or oil has been known and is referred to as a "flavor oil" or "seasoning oil". For producing such a flavor oil or seasoning oil, there have been proposed various methods. For example, the proposed methods include a method for producing a flavor oil having a characteristic flavor of Chinese dishes such as pan-fry or deep-fry dishes which comprises adding fennel, Welsh onion and garlic into a fat or oil heated with flames having strong caloric force to extract their essence sufficiently, lowering the temperature, adding pepper to the mixture to further extract their essence and then filtering off the oil (Japanese Patent Kokoku No. 57-58901); a method for producing flavor oils having various flavors which comprises cutting or grinding vegetables having a water content of 60% or higher, for example, such as cabbage, lettuce, ginger, garlic, Welsh onion and the like into pieces of less than 2 mm in thickness, adding the vegetables to a fat or oil, maintaining the mixture at 110.degree. to 160.degree. C. and then collecting the oil phase (Japanese Patent Kokoku No. 59-4972); a method for producing a seasoning oil for various dishes such as steak, sukiyaki, sauteed vegetables, Chinese noodles, Chinese-style hotchpotch, gratin, soup and the like which comprises dipping raw materials to be treated such as vegetables into a heated oil in a cooker to conduct a heat treatment and, at the same time of heating, subjecting the mixture to a treatment at reduced pressure under constant conditions to dissolve their essence, flavors and other ingredients in the oil and then taking the oil out from the cooker (Japanese Patent Kokai No. 60- 19449): and a method for producing flavor oils having various flavors which comprises subjecting an admixture of a fat or oil and raw materials such as vegetables, meat, fowl, fishery products, seaweeds, spices, beans, a processed product thereof or a mixture thereof with a flavoring material such as a brewed product, to heat treatment under a normal pressure, and then subjecting the resultant product to a heat treatment under pressure (Japanese Patent Kokai No. 62-6651).
All of these conventional methods for producing a flavor oil or seasoning oil utilize flavor components possessed by the flavoring materials such as flavor, smell and the like and, although the flavor oils themselves are good products, they have their own peculiar flavors and, therefore, there is a disadvantage that their uses are limited.
On the other hand, apart from a flavor oil or seasoning oil, although edible fats and oils purified by a conventional method are almost tasteless and odorless as described above, in fact, they have their own peculiar oily flavor. For example, in general, a liquid oil has a peculiar fatty flavor and palm oil has a peculiar powdery flavor. Therefore, there is a disadvantage that they have unpleasant oily flavor, and such an unpleasant oily flavor increases with time.
Further, as a frying oil, for example, there can be normally used soybean oil, rapeseed oil, palm oil, palm soft oil and the like. However, these oils contain a large amount of unsaturated acids as the constituent fatty acids and, therefore, peroxides, carbonyl compounds and the like are formed during frying and there is a problem of thermal oxidation stability. For solving this problem, for example, hardening of these oils can normally be employed to improve thermal oxidation stability and storage oxidation stability. However, when using these hardened oils (hydrogenated oils) for frying, there is a disadvantage that a peculiar smell is formed by hardening and, therefore, it is not preferred in view of flavor.